A communication cable may extend for five miles within a city and the cable extends through a conduit and manhold system having perhaps a large number of laterals and stubbed splices within the same physical cable or to other cables within the communications system. The cable is internally pressurized with air at a pressure of perhaps 4 pounds above atmospheric pressure. Air is usually introduced under pressure into the cable at one end thereof and while the internal pressure may be 4 pounds at one end of the cable it may be only 2 pounds or less at the far end of the cable. Thus, a flow of air exists in the cable from the high pressure end thereof to the low pressure end thereof.
If, at a point between the opposite ends of the cable a splice is included to an aerial lead and it is desired that the pressure of air within the cable not extend to the aerial lead, a plug is poured in the aerial lead to avoid unnecessary loss of air pressure which is necessary and vital to the underground cable system, as air pressure aids in eliminating or avoiding the entry of foreign matter such as liquids into the underground cable.
In order to plug the aerial lead a quantity of hardenable thick liquid substance is injected into the aerial lead and once the liquid has hardened a solid air-tight plug will be formed. However, if the slightest amount of air flow exists within the aerial lead at the time the injected hardenable liquid is curing, air trails will be formed within the hardening liquid and will create a leak destroying the intended purpose of the plug.
The method and apparatus of the instant invention have been specifically designed to function in the capacity of maintaining air pressure within the aerial lead equal on opposite sides of the poured plug during the curing of the plug so as to eliminate any air trails through the plug.
Apparatuses similar in structure to the instant invention, but different and provided for other purposes have been heretofore designed. Examples of these previous apparatuses may be found in U.S. Pat. Nos. 2,043,227 to C. E. Bennett, dated June 9, 1936 and 2,449,271 to C. E. Bennett et al, dated Sept. 14, 1948.
The main object of this invention is to provide a method and apparatus for establishing and maintaining equal air pressure on opposite sides of a plug being formed in a communications cable.
Another object of this invention is to provide a method and apparatus for checking the seal established by a plug formed in a communications cable.
Yet another object of this invention is to provide a method and apparatus for establishing a bypass around a plug formed in a communications cable.
A final object of this invention to be specifically enumerated herein is to provide a method and apparatus in accordance with the preceding objects with the apparatus conforming to conventional forms of manufacture being of simple construction and easy to use so as to provide a device that will be economically feasible, long lasting and relatively trouble free in operation.